My 2002 king cab Frontier with K24ED and manual with 131,000 miles has a noticeable whine or hum when in 5th at 50-70 mph. In 3rd or 4th its not noticeable but on shifting to 5th and cruising or under load it's there. Not when coasting against compression. Have drained and refilled both trans and rear end with proper fluids / GL 4 Redline MT 90 in trans and Valvoline GL 5 75-80 in rear end, full synthetics in both.
NO accumulation of metal particles on either magnet drain plugs when serviced and prior service interval on both was at 80K. NO excessive backlash or play in rearend /ujoints /center support bearing / rear axle bearings.
Has anyone experienced this with their truck? If so, was the solution for a bearing /syncro /seal overhaul of the trans?
Thanks for any thoughts on this.